生物钻孔改良黏质红壤及提高作物抗旱能力的潜力与机制

In the red soils area of subtropical China, the seasonal drought often occurs in summer and autumn due to the water shortage in surface soil, despite the relative abundant water in deeper subsoil. But the water in deep subsoil is unlikely to be absorbed by crops because their roots are usually limited in the shallow layer. In the clayey red soils, the subsoil is often dense and compact with high mechanical resistance and poor aeration, it thus restrains the crop root penetrating into deep subsoil. This kind of conflict between root growth and soil property usually induces and increases the crop drought stress in dry season. It is hypothesized that the plant breed with strong penetrability can drill the clayey red soil (penetrate into subsoil) and produce bio-pore in subsoil. It is proposed that bio-drilling can increase the porosity of the subsoil, and promote the crop root to penetrate into deeper soil and absorb more soil water, thus improve the crop drought-resistance ability in the next growth season. In the present proposal, three varieties of green manure- and forage- plants, namely lucerne, vetiver grass, and deep root rapeseed, all of which are characterized by strong root and expected to penetrate into the clayey subsoil, will be employed as drilling-crops in the “pre-crop - maize crop” rotation experiment in field plots. In this four-year crop rotation experiment, the bio-drilling ability of the three varieties and their effects on soil improvement will be analyzed by measuring bio-pore and soil physical properties. The interaction of “root - soil pore” and “root - soil matrix” will be investigated by measuring the root morphology and root distribution in the soil profile. The effects of bio-drilling on the crop drought resistance will be verified by measuring the maize crop water uptake from the soil, crop performance and drought stress severity. The results are expected to understand the interaction of “root - soil” in the clayey red soil from the view of soil physics, thus to provide new theoretical basis for seasonal drought defense in the red soils area.

我国亚热带红壤区的夏秋季节性干旱往往发生在土壤浅层，深层并不缺水，但黏质红壤心土紧实，机械阻力大，通气状况差，导致作物根系分布浅，限制其利用深层土壤水分，这种 “根-土”矛盾是作物容易受旱的重要原因。因此设想利用生物钻孔改良红壤，改善底土孔隙状况，促进后季作物根系下扎分布以吸收更多深层土壤水分，从而提高作物的抗旱能力。项目以紫花苜蓿、香根草、深根系油菜等几种钻孔能力强的牧草和绿肥作为前季植物，开展“前季钻孔植物-后季玉米作物”的多季轮作田间试验，测定生物孔隙特征和土壤物理性质，评价钻孔植物在黏质红壤的钻孔能力和改土效果；测量作物根系空间分布和形态特性，揭示“根系-土壤孔隙”及“根系-土壤基质”的相互作用特征；监测作物土壤水分吸收、生长状况和干旱程度，探明生物钻孔对作物抗旱能力的影响。研究结果有望从土壤物理的角度揭示黏质红壤的“根-土”相互作用特征和调控潜力，为季节性干旱防御提供理论依据。

我国红壤区的季节性干旱对农业生产危害很大，研究红壤季节性干旱发生和发展规律和有效防御措施具有重要意义。理论上红壤性质不良导致作物根系浅而难以利用深层土壤水分是加剧干旱的原因之一，而前季植物根系的钻孔作用可促进后季作物根系下扎提高其抗旱能力，是有潜力的干旱防御途径。本项目的研究目的是探明生物钻孔改良黏质红壤物理性质和提高后季作物抗旱能力的潜力，从“根-土”相互作用的角度揭示生物钻孔防御红壤季节性干旱的机制。项目选择了普通油菜、深根系油菜、紫花苜蓿、香根草等4种秋冬季生长的植物为钻孔植物，通过4年“钻孔植物-玉米作物”轮作的田间试验，研究了它们在黏质红壤中的钻孔能力与根系分布特征、对红壤耕层及犁底层物理性质的改良作用、对后季玉米作物“根-土”关系的影响、改善后季玉米作物抗旱能力的潜力。取得的主要结果有：(1)几种钻孔植物根系在黏质红壤中表现出不同的形态和钻孔性能，钻孔植物的平均根径和下扎深度差异巨大，这为解释其在土壤中的分布和改良效果、为选择合适的轮作钻孔植物提供了理论依据；(2)生物钻孔显著改善了黏质红壤的理化和生物性质，根系越多的土层(0-20 cm)改善效果越好，其中深根系钻孔植物紫花苜蓿和香根草能改良深层(20-60 cm)土壤性质；(3)生物钻孔改善了后季玉米作物“根-土”关系，表现为降低了各个土层的容重和穿透阻力，增加了土粒间微观作用力利于土壤水稳定性团聚体形成，扩大了黏质红壤的最小水分限制范围，促进了后季玉米根系下扎；(4)生物钻孔改善了后季玉米作物抗旱能力，增加了对深层土壤水分(20-60 cm)的吸收，改善了作物干旱时期的作物水力结构，降低了玉米水分胁迫指数，在干旱年份显著降低了玉米作物的产量损失，4种供试钻孔植物中，以紫花苜蓿和多年生香根草效果较好。研究结果证实了改良深层红壤物理性质可以改善作物根土关系，为红壤季节性干旱防御提供了理论和技术途径。项目发表SCI论文5篇，培养研究生6名。